A. Field of Invention
This invention relates to a method and apparatus for grinding stumps with an elongated grinding tool rotatable about a generally vertical axis. The tool is mounted on a supporting vehicle which may be self powered or the supporting vehicle may provide power for rotating the tool. Piston cylinder assemblies on the vehicle provide vertical movement of the grinding tool into and out of the ground adjacent the stump and horizontal movement along the sides of the stump for grinding the stump.
B. Description of Related Art
Stump grinders of the type shown in applicant's U.S. Pat. No. 6,435,234 have disc cutters rotatable about a generally horizontal axis and are moved through the stump in a direction parallel with the axis of the cutter. This has the disadvantage of the drive shaft and bearings being below the ground level where they are exposed to dirt and rocks. Also, the debris which may include stones is thrown out of the hole in the ground which constitutes a safety problem.
Another problem with disc cutters rotatable about a horizontal axis is that they require relatively large diameter disc cutters in order to grind deep enough to remove the roots of medium and large stumps. The large diameter disc cutters require more power which cannot be supplied by small horsepower vehicles. The large diameter discs also may climb up on the stump being ground and upset the vehicle on which they are mounted.
Stump grinding tools rotatable about a vertical axis have been proposed as shown in U.S. Pat. Nos. 1,012,962 and 1,466,538 where the grinding tools are placed over the stump and grind it down to ground level. These patents including U.S. Pat. No. 3,818,957 which has a grinding tool rotatable about a vertical axis are directed to brush and tree cutting for land clearing and not to stump removal. Also, as stated in U.S. Pat. No. 3,818,957 “a shroud can be affixed to the outer portions of these elongate blades to retain dirt or earth removed by the blades at the sight—” This clearly indicates the grinding is done above the ground and not below the ground.